It is know from the journal "Funkschau", volume 25, page 53, 1985, to process and reproduce a composite video signal digitally. In this system the composite video signal is converted to digital form in an analog-to-digital converter and then split into the components of the luminance signal Y and the chrominance components U and V in a digital color decoder. In order to avoid an excessive number of connections the signals are transmitted in time multiplexed fashion and subsequently stored in picture memories.
In picture-in-picture systems wherein images from one video source are to be displayed within images from another video source, the video signals from the first source are typically split into components parts and then applied to analog-to-digital converters. Desirably only a single analog-to-digital converter is used by multiplexing the analog video components thereto. However, problems arise in multiplexing the components to a single converter. For example the analog-to-digital converter must operate at a high sampling rate in order to produce a picture of acceptable resolution.
There are several solutions to appropriately multiplexing the component video signals to a single converter. For example, the analog video component signals may be sampled and multiplexed to form horizontal lines of signal in the form of YUYV sampled data where Y is the luminance signal and U and V are the chrominance signal parts (U=B-Y, V=R-Y). These sequences of sampled data are applied to the analog-to-digital converter which generates their digital counterparts. The digital values are written to memory at a first frequency rate, and read out at a higher frequency rate to achieve horizontal compression of the image. For vertical compression only one out of every set of three or four horizontal lines of the video input signal is analyzed. The reduction ratio is selected dependent on the desired result. If necessary, the signal is applied to a vertical filter.
The signal read from memory is applied to three digital-to-analog converters to reproduce the compressed Y, U and V signals. Subsequently, the compressed signals are substituted for portions of the main video signal.
The concepts developed to date provide picture-in-picture processing for TV signals requiring a reduced number of circuit connections. However, a relatively high multiplexing frequency is used in order to obtain a correct signal bandwidth for each video component.
It is an object of the present invention to provide a circuit for processing a picture-in-picture video signal at reduced cost.